Chemical process and composition

ABSTRACT

The invention relates to a process for production of hydrogen peroxide according to the anthraquinone process including alternate hydrogenation and oxidation of one or more quinones selected from anthraquinones and/or tetrahydro anthraquinones in a working solution comprising at least one quinone solvent and at least one hydroquinone solvent, wherein said at least one quinone solvent comprises isodurene in an amount from 15 to 100 wt %. The invention also relates to a composition useful as a working solution at production of hydrogen peroxide.

This application claims the benefit of Ser. No. 60/212,633, filed Jun.19, 2000.

The present invention relates to a process for production of hydrogenperoxide according to the anthraquinone process, wherein the workingsolution comprises a certain mixture of solvents. The invention alsoconcerns a composition comprising such a mixture of solvents that isuseful as a working solution at production of hydrogen peroxide.

The most common process for production of hydrogen peroxide is theanthraquinone process. In this process quinones selected from optionallysubstituted anthraquinones and/or tetrahydro anthraquinones dissolved ina suitable organic solvent mixture, a so called working solution, arehydrogenated to form the corresponding hydroquinones. The hydroquinonesare then oxidised back to quinones with oxygen (usually air) withsimultaneous formation of hydrogen peroxide, which then can be extractedwith water while the quinones are returned with the working solution tothe hydrogenation step.

The anthraquinone process is described extensively in the literature,for example in Kirk-Othmer, “Encyclopedia of Chemical Technology”,4^(th) Ed., 1993, Vol. 13, pp. 961–995.

For the process to work properly, it is necessary to use a solventmixture for the working solution in which both quinones andhydroquinones are soluble. Therefore, the solvent mixture in the workingsolution normally comprises one or more quinone solvents and one or morehydroquinone solvents.

The problem of finding suitable solvents for the working solution hasbeen addressed in, for example, U.S. Pat. Nos. 3,328,128, 4,800,073 and4,800,074, and GB patent 1524883.

In many cases, the production capacity in a plant is limited by theamount of quinones available for hydrogenation in the working solutionor the amount of hydroquinones that can be formed without precipitationthereof. This problem has been found to be of particular importance whenthe amount of tetrahydro anthraquinones in the working solution is high.

Thus, there is a demand for a working solution based on a solventcombination with improved solubility of both quinones and hydroquinones,particularly of tetrahydro anthraquinones. Furthermore, it is desirableto provide a working solution with comparatively low density, whichfacilitates the phase separation at an extraction step performed afterthe hydrogenation and oxidation steps.

It has now been found possible to provide a working solution fulfillingthese demands by selecting a certain combination of solvents.

Thus, the invention concerns a process for production of hydrogenperoxide according to the anthraquinone process including alternatehydrogenation and oxidation of one or more quinones selected fromanthraquinones and/or tetrahydro anthraquinones in a working solutioncomprising at least one quinone solvent and at least one hydroquinonesolvent, wherein said at least one quinone solvent comprises isodurene(1,2,3,5-tetramethylbenzene) in an amount from 15 to 100 wt %,preferably from about 20 to about 80 wt %, most preferably from about 25to about 70 wt %.

Most preferably the at least one quinone solvent referred to abovesubstantially consists of one or more essentially non-polar organicsolvents, preferably hydrocarbons, while the at least one hydroquinonesolvent referred to above most preferably substantially consists of oneor more polar organic solvents, suitably essentially non-soluble inwater and preferably selected from alcohols, ureas, amides,caprolactams, esters, phosphorus containing substances and pyrrolidones.

It has been found that when the proportion of isodurene compared toother optional quinone solvents is high, the solubility of quinones isimproved to such an extent that it is possible to decrease the totalamount of quinone solvents in the working solution and instead increasethe amount of hydroquinone solvents, and thereby increase the solubilityof both quinones and hydroquinones.

In addition to isodurene, the at least one quinone solvent suitablycomprises durene (1,2,4,5-tetramethylbenzene), wherein the total amountof isodurene and durene suitably constitutes from about 30 to about 100wt %, preferably from about 35 to about 80 wt % of the total amount ofquinone solvents. In order to avoid precipitation of durene the contentthereof should not be too high, preferably not exceeding about 25 wt %,most preferably not exceeding about 20 wt % of the total amount ofquinone solvents. The weight ratio isodurene to durene in the workingsolution is preferably from about 1.5:1 to about 5:1, most preferablyfrom about 2:1 to about 4:1.

The at least one quinone solvent may also comprise other suitablyessentially non-polar hydrocarbons, preferably selected from one or morearomatic, aliphatic or naphthenic hydrocarbons, of which aromatichydrocarbons are most preferred. Particularly suitable quinone solventsinclude benzene, alkylated or polyalkylated benzenes such astert-butylbenzene or trimethyl benzene, alkylated toluene or naphthalenesuch as tert-butyltoluene or methylnaphthalene.

The preferred total content of quinone solvents and consequently alsothe content of isodurene used in the entire working solution depends onwhich hydroquinone solvent(s) that are used. In most cases, the suitablecontent of quinone solvents is from about 25 to about 65 wt %,preferably from about 40 to about 60 wt % of the entire workingsolution. In most cases, the weight ratio quinone solvents tohydroquinone solvents suitably is from about 0.6 to about 4, preferablyfrom about 1.5 to about 3. The suitable content of isodurene normally isfrom about 8 to about 52 wt %, preferably from about 11 to about 42 wt %of the entire working solution.

The working solution comprises at least one and preferably at least twohydroquinone solvents, suitably selected from polar organic solvents,which, however, preferably should be essentially non-soluble in water.Suitable hydroquinone solvents may be selected from alcohols, ureas,amides, caprolactams, esters, phosphorus containing substances andpyrrolidones, and include alkyl phosphates (e.g. trioctyl phosphate),alkyl phosphonates, alkylcyclohexanol esters, N,N-dialkyl carbonamides,tetraalkyl ureas (e.g. tetrabutyl urea), N-alkyl-2-pyrrolidones and highboiling alcohols, preferably with 8–9 carbon atoms (e.g. di-isobutylcarbinol). Preferred hydroquinone solvents are selected from alkylphosphates, tetraalkyl ureas, cyclic urea derivatives andalkyl-substituted caprolactams. One group of preferred hydroquinonesolvents are described in the U.S. Pat. Nos. 4,800,073 and 4,800,074 andinclude alkyl-substituted caprolactams such as octyl caprolactam andcyclic urea derivatives such as N,N′-dialkyl-substituted alkylenurea.Other preferred hydroquinone solvents include di-isobutyl carbinol andtetrabutyl urea, which are advantageous in the sense that they have lowdensity.

The content of hydroquinone solvents in the working solution ispreferably from about 15 to about 48 wt %, most preferably from about 18to about 35 wt %.

The anthraquinones and tetrahydro anthraquinones in the working solutionto be hydrogenated are preferably alkyl substituted, most preferablywith only one alkyl group, suitably at the 2-position. Preferred alkylsubstituents include amyl such as 2-tert-amyl or 2-iso-sec-amyl, ethyl,tert-butyl and 2-hexenyl, and it is particularly preferred that at leastethyl substituted anthraquinones and/or tetrahydro anthraquinones areincluded. Preferably the working solution to be hydrogenated include amixture of different alkyl substituted anthraquinones and tetrahydroanthraquinones, more preferably a mixture of ethyl and at least oneother alkyl substituted, most preferably amyl substituted anthraquinoneand/or tetrahydro anthraquinone. Preferably from about 50 to about 100mole %, most preferably from about 60 to about 90 mole % of theanthraquinones and the tetrahydro anthraquinones are substituted withone ethyl group. It is also preferred that up to about 50 mole %, mostpreferably from about 10 to about 40 mole % of the anthraquinones andthe tetrahydro anthraquinones are substituted with one amyl group.

It has been found favourable to operate at high amounts of tetrahydroanthraquinones compared to anthraquinones, as it then is possible toachieve high degree of hydrogenation and low losses of active quinonesto degradation products. Suitably the molar ratio of tetrahydroanthraquinones to anthraquinones in the working solution to behydrogenated exceeds 1:1 and is preferably from about 2:1 to about 50:1,most preferably from about 3:1 to about 20:1. In some cases it may beappropriate to operate at a molar ratio only up to about 9:1, but it isalso possible to use working solutions almost free from anthraquinones.

The molar ratio of tetrahydro anthraquinones to alkyl anthraquinones ina mature working solution (a working solution used for hydrogen peroxideproduction during at least six months) is suitably in the same magnitudefor the anthraquinones substituted with different groups. The molarratio for each group differ preferably less than with a factor of about2.5, most preferably less than with a factor of about 1.7.

The tetrahydro anthraquinones are normally mainly made up ofβ-tetrahydro anthraquinones, but also some α-tetrahydro anthraquinonesmay be present.

Besides the direct or indirect hydrogenation to hydroquinones, manysecondary reactions take place. For example, the anthrahydroquinones canreact further to tetrahydro anthrahydroquinones, which in the oxidationstep is converted to tetrahydro anthraquinones, the content of whichthus will increase in the working solution. This means that when theprocess of the invention is started up, the initial working solution maycontain no or only small amounts of tetrahydro anthraquinones, as theywill form automatically during the course of operation. As soon as thedesirable concentrations of anthraquinones and tetrahydro anthraquinoneshave been reached, at least a portion of the working solution is thennormally treated to dehydrogenate tetrahydro anthraquinones back toanthraquinones.

It also occurs direct or indirect formation of unwanted by-products,such as epoxides, octahydro anthraquinones, oxanthrones, anthrones anddianthrones. Some of these compounds, like epoxides can be convertedback to anthraquinones, while others, like dianthrones, constitute anirreversible loss of active working solution. It has been found that theformation of undesired by-products can be minimised if the molar ratioof tetrahydro anthraquinones to anthraquinones is maintained within theabove specified range.

The high amounts of isodurene in the working solution renders itpossible to dissolve high amounts of ethyl substituted tetrahydroanthraquinone, which has lower density than, for example, the highlysoluble amyl substituted tetrahydro anthraquinone. It is then possibleto combine high concentration of quinones available for hydrogenation inthe working solution with low density, thus increasing the productioncapacity of hydrogen peroxide per volume working solution. The totalamount of anthraquinones and tetrahydro anthraquinones in the workingsolution to be hydrogenated is preferably from about 15 to about 28 wt%, most preferably from about 17 to about 25 wt %, while the densitymeasured at 20° C., preferably is from about 910 to about 980 kg/m³,most preferably from about 930 to about 970 kg/m³.

The hydrogenation step is normally performed by contacting the workingsolution with hydrogen gas in the presence of a catalyst at atemperature from about 0 to about 100° C., preferably from about 40 toabout 75° C., and at an absolute pressure from about 100 to about 1500kPa, preferably from about 200 to about 600 kPa. The degree ofhydrogenation (as moles hydroquinones per m³ working solution) issuitably from about 350 to about 800, preferably from about 400 to about650.

The active catalyst may, for example, be a metal selected from any ofnickel, palladium, platinum, rhodium, ruthenium, gold, silver, ormixtures thereof. Preferred metals are palladium, platinum and gold, ofwhich palladium or mixtures comprising at least 50 wt % palladium areparticularly preferred. The active catalyst may be in free form, e.g.palladium black suspended in the working solution, or be deposited on asolid support such as particles used in the form of a slurry or a fixedbed. However, it is particularly preferred to use a catalyst in the formof an active metal on a monolithic support, for example, as described inU.S. Pat. Nos. 4,552,748 and 5,063,043. Preferred support materials areselected from silica or aluminium oxide.

Before or after the hydrogenation step, at least a portion of theworking solution is preferably regenerated in one or several steps toremove water, to keep the desired ratio of tetrahydro anthraquinones toanthraquinones, to convert some undesired by-products from thehydrogenation or the oxidation steps back to active components, and toremove other undesired by-products. The regeneration may includefiltration, evaporation of water, and treatment with a porous adsorbentand catalyst based on aluminium oxide.

Other steps in the overall process of producing hydrogen peroxide, suchas oxidation with oxygen or air and extraction with water, may beperformed in conventional manner as described in the literature.

The invention further concerns a composition useful as a workingsolution at production of hydrogen peroxide with the anthraquinoneprocess. The composition comprises one or more anthraquinones and/or oneor more tetrahydro anthraquinones dissolved in at least one quinonesolvent, and at least one hydroquinone solvent, wherein said at leastone quinone solvent comprises isodurene in an amount from 15 to 100 wt%, preferably from about 20 to about 80 wt %, most preferably from about25 to about 70 wt %. Regarding optional and preferred features of thecomposition, the above description of the process is referred to.

The invention will now further be described in connection with thefollowing Examples, which, however, not should be interpreted aslimiting the scope of the invention.

EXAMPLE 1

The solubility of β-tetrahydro ethyl anthraquinone was measured in twodifferent pure quinone solvents:

Solvent: Regular mixture Isodurene Technical grade aromatic (mixturecomprising 69 wt % hydrocarbons isodurene, 22 wt % durene), 9 (mainlyC₁₀ + C₉) wt % other C₁₀ aromatic (Shellsol ™ AB) hydrocarbonsSolubility at 20° C. 115 g/liter 180 g/liter

EXAMPLE 2

Two different mature working solutions, A (comparative) and B (theinvention), were tested in an anthraquinone process, the solutions thusalso containing normal degradation products. Both solutions comprisedtetrabutyl urea as hydroquinone solvent and 2-ethyl and 2-amylsubstituted anthraquinones and tetrahydro anthraquinones (the molarratio 2-ethyl to 2-amyl exceeded 1:1 and was maintained constant). Themolar ratio tetrahydro anthraquinones to anthraquinones exceeded 3:1.

The main difference between the working solutions was that in Solution Athe quinone solvent was made up of ShellSol™ AB, a regular mixture ofaromatic hydrocarbon with mainly C₁₀ and C₉ alkyl-benzene (about 85%),while in Solution B the quinone solvent instead was made up of 40 wt %Shellsol™ AB mixed with 60 wt % of isodurene (Technical grade comprisingabout 69% isodurene, about 22% durene and about 9 wt % other C₁₀aromatic hydrocarbons).

In both cases the total content of tetrahydro anthraquinones andanthraquinones were kept as high as possible to reach highconcentrations of hydrogen peroxide in the working solution. However,precipitation β-tetrahydro ethyl anthraquinone and/or its hydroquinoneform in the working solution was a limiting factor.

More data are shown in the table below:

Working solution: A B Isodurene as wt % of quinone solvent 10% 45%Isodurene as wt % of working solution  5% 21% Durene as wt % of quinonesolvent  7% 16% Tetrabutyl urea as wt % of working 22% 25% solutionDensity of working solution (20° C.) 950 kg/m³ 960 kg/m³ Total contentof tetrahydro 122% relative A anthraquinones and anthraquinones (about18–23 wt %) Hydrogen peroxide limit in working 125% relative A solutionIt was thus possible to operate working solution B with a higherproduction capacity than solution A.

1. A process for production of hydrogen peroxide according to the anthraquinone process including alternate hydrogenation and oxidation of one or more quinones selected from the group consisting of anthraquinones and tetrahydro anthraquinones, in a working solution comprising at least one quinone solvent tetrabutyl urea, wherein said at least one quinone solvent comprises isodurene in an amount from about 20 to about 80 wt % and additionally durene in an amount not exceeding about 25 wt % of total amount of quinone solvents, the total amount of isodurene and durene constituting from about 30 to about 100 wt % of the quinone solvents, and further wherein the weight ratio isodurene to durene in the working solution is from about 1.5:1 to about 5:1.
 2. A process as claimed in claim 1, wherein the density, measured at 20° C., is from about 910 to about 980 kg/m³.
 3. A process as claimed in claim 1, wherein the molar ratio of tetrahydro anthraquinones to anthraquinones in the working solution to be hydrogenated exceeds 1:1.
 4. A process as claimed in claim 3, wherein the molar ratio of tetrahydro anthraquinones to anthraquinones in the working solution to be hydrogenated is from about 2:1 to about 50:1.
 5. A process as claimed in claim 1, wherein from about 50 to about 100 mole % of the anthraquinones and the tetrahydro anthraquinones are substituted with one ethyl group. 